Project Summary Over the last 6-7 years, Direct Oral Anticoagulants (DOACs) have become increasingly prevalent for treating patients with cardiovascular disorders because of their pharmacokinetic stability and lack of interaction with certain foods. Yet, there is increasing evidence of improper dosing in a small proportion of treated patients, and growing recognition of the need to develop simple, inexpensive tests to measure DOAC effects for acute blood-loss trauma or embolic events. There is currently no single assay which fulfills these needs and provides the requisite levels of accuracy and sensitivity to quantify all DOACs. This application presents prelim- inary data from a modified dilute PT assay which displays highly sensitive clotting-time responses to Dabiga- tran, Rivaroxaban, and Apixaban, which we have named the ?Extrinsic Pathway Clot Time (EPCT)? Assay. The key components of the EPCT are re-lipidated tissue factor (TF) triggering agent (E-plastin), and the specif- ic Factor XIIa inhibitor, corn trypsin inhibitor (CTI), which blocks contact pathway activation in collected blood samples, allowing long artifact-free clot times. The goal of this proposal is to fine-tune the EPCT Assay to prov- ide a simple-to-execute, ?universal? technique which can be performed on standard laboratory coagulometers, and allows timely, sensitive, unambiguous measurements of the pharmacodynamic effects of DOACs. In Aim 1, a variety of E-Plastin reagents with variations in phospholipid content and composition will be synthesized in-house using recombinant, expressed rabbit TF, and characterized in-vitro. After determination of the optimal dilution levels to give the DOAC-free long clot times needed for optimal sensitivity, dose-res- ponse curves to DOAC-spiked blood taken from a number of healthy subjects will then be acquired for the various E-Plastin preparations, using both mechanical detection of clotting in whole blood, and optical detec- tion in plasma. Results for the direct FXa inhibitors will be compared with chromogenic assays which quantify mass level. We will perform statistically-weighted comparisons of the slope of the response for different subjects to different DOACS while addressing the following questions. 1) How much impact do the variations in E-Plastin composition have on response sensitivity (curve slope) to a given DOAC within and between subjects? 2) Are the sensitivities of response curves to different DOACs significantly different when using a single E-Plastin for individual subjects? 3) Are the dose-response curve slopes to a specific DOAC significantly different between subjects when averaged over multiple times of assay performance for a given E-Plastin? (25) In Aim 2, we will collaborate with Dr. Schneider to use the EPCT assay for measurements on samples from patients suffering with various disorders (especially atrial fibrillation), who are being treated with DOACs, anti-platelet agents, and Warfarin. The goal of these studies will be to determine whether the EPCT assay can be used to enhance the ability of the clinician to spot patients at higher risk for bleeding or embolic events, allowing them to correctly adjust dosing to decrease the prevalence of these adverse outcomes.